Note: Descriptions are shown in the official language in which they were submitted.
STRIPPER RUBBERS FO_
DRILLING HEADS
Backqround Of The Invention
I. Field of the Invention
This invention relates to stripper rubbers used to se21
against a drill string deployable through a drilling head
and, in particular, to a rein~orced stripper rubber for
preventing extrusion of the stripper under pressure and
reducing the tensile and compressive stresses on the
stripper rubber.
II. Descri tion of the Prior ~rt
P
Drilling heads are widely used in drilling operations
to prevent the drilling fluids from flowing out onto the rig
floor. The typical drilling head incorporates a diverter
passageway for diverting the drilling fluids, a rotatable
drive assembly with bearings to rotate with or drive the
drill string, and a stripper rubber positioned within the
drilling head. The stripper rubber may be secured to the
rotating drive assembly in order to rotate with the drill
string and seal against the string to prevent drilling
fluids from flowing up through the drilling head. The
stripper rubber must be resilient enough to allow various
tools and couplings to pass through the drilling head while
maintaining the seal. More recent drilling heads have
incorporated two axially separated stripper rubbers to
maintain the seal thereby preventing fluid flow through the
drilling head.
Prior known drilling heads have incorporated stripper
rubbers of varying sizes and shapes in order to maintain the
desired sealing en~agement under the fluid pressures found
2 ~
in drilling operations. The single greatest disadvantage of
prior known stripper rubbers is their tendency to extrude
and invert or ~asshole~ under extreme pressures. In the
typical assambly, the stripper rubber is mechanically
restrained only by the insert at the top o~ the drilling
head. As a tool joint of the drill pipe is lowered through
the drilling head, the stripper rubber i5 pulled in tension
and elongates severely until the tool joint has passed
through the rubber. Such stretching and elongation results
in high stress loads on the stripper rubber. When fluid
pressure is applied to the stripper rubber, the rubber is
loaded in compression. Since the lower portion of the
stripper is unsupported, the rubber can extrude and invert.
This problem is exacerbated as a drill string joint is being
drawn upwardly thro~yh the stripper rubber.
Attempts to eliminate inversion of the stripper rubber
have included increasing the strength of the materials and
the thickness of the stripper rubber. However, such changes
affect the resiliency of the stripper rubber and thersfore
the ability to maintain the proper seal against the varying
thicknesses of the drill string.
Different stripper rubbers have been developed for
di~ferent applications according to the environment and
workload placed upon the rubber. ~Shortyn stripper rubbers
have been developed for use in minimal clearance drilling
h~ads. High Pressure and Heavy Duty stripper rubbers are
used in specialized applications. Thus, a single stripper
rubber capable of use in the various drilling heads is
needed.
Summary Of The Present Invention
Tha present invention overcomes the disadvantages of
the prior known stripper rubbers by providing a stripper
rubber which is reinforced to prevent extrusion and
Z
7~
inversion whi]e malntaining the resilient properties required to
ensure sealing engagement with the drill pipe as it passes
through the drilling head.
This invention relates to a stripper rubber for use in
a well drilling head having a drill string selectively extending
therethrough, said stripper rubber comprising: a stripper body
havin~ an axial passageway, said stripper body selectively
sealingly engaging the drill string extending through said axial
passageway and the drilling head; and means for restraining said
stripper body against deformation within the drilling head~
The present invention provides three preferred embodi-
ments of a stripper rubber for a drilling head which incorporates
reinforcement means to reduce the tensile and compressive
stresses while eliminating extrusion under pressure. In a Eirst
embodiment, the stripper rubber is vertically restrained by bars
which extend between upper and lower rings molded into the
stripper rubber. The bars restrain the rubber in the vertical
direction but radial expansion is unrestrained to allow tool
joints to pass through the drilling head in sealing engagement
~0 with the stripper rubber. A second embodiment incorporates
reinforcement cords into the stripper rubber to increase the
longitudinal strength.
A still further embodiment bonds the stripper rubber
into a metal cylinder which acts to restrain the rubber in the
vertical direction. Radial deflection as a tool joint passes
through the rubber is accommodated by allowing the rubber material
to flow vertically.
~ J ¦"~ 'b6/~
. .:, "
,'~
: '
,.
72290~
These stripper rubbers may be mounted into the drilling
head using a conventional drive bushing assembly or alternatively
using an integral drive bushing which is molded directly into the
top of the s-tripper rubber thereby eliminating the conventional
bolt and ring assembly. By incorporating the drive bushing into
the stripper rubber reliability and durability are substantially
increased. Moreover~ the socket screws of the conventional
mountings are eliminated reducing the number of parts.
Other objects, features, and advantages of the invention
will be apparent from the following detailed description taken in
connection with the accompanying drawings.
3a
2~$~
Brief Description Of The Drawinq
The present invention will be more fully understood by
reference to the following detailed description of a
preferred embodiment of the present invention when read in
conjunction with the accompanying drawing, in which like
reference characters refPr to like parts throughout the
views and in which:
FIGURE 1 is a partial cross sectional view of a
drilling head incorporating one embodiment of the stripper
rubber of the present invenkion;
FIGURE 2 is a cross-sectional perspective of the
stripper rubber,
FI~URE 3 is a lateral cross-sectional view taken along
lines 3 3 of Fig. l;
FIGURE 4 is a partial perspective view of the
reinforcing structure molded into the stripper rubber of the
present invention;
FIGURE 5 is a cross sectional perspective of another
embodiment of the stripper rubber of the present invention;
FIGURE 6 is a cross-sectional perspective of a still
further embodi~ent o~ the stripper rubber of the present
invention; and
FIGURE 7 is a partial cross-sectional view of an
integral drive bushing for ~ stripper rubber.
Detailed Description Of A Preferred
Embodiment Of The Present Invention
_ _
Referring first to Figure 1, there is shown a drilling
head 10 for use in well drilling operations and which
incorporates a stripper rubber 12 embodying the present
invention. The stripper rubber 12 is preferably removably
received within the drilling head 10 for selective
replacement as it b~comes worn or for insertion of a
different stripper nlbber 12 to accommodate different
operations and/or enYironments. The stripper rubber 12 may
be stationary within the drilling head 10 or may rotate
substantially in conjunction with a drill string (now shown)
extending through the drilling head 10 and the stripper
rubber 12. The stripper rubber 12 is designed to sealingly
engage the drill string, including any greater diameter tool
joints, as it passes through the drilling head 10 to prevent
drilling fluids from flowing up through the drilling head 10
onto the rig floor. Most dri1ling heads 10 are pxovided
with a diverting passageway to divert the drilling fluids
from the rig. Thus, the stripper rubber 12 must be
resilient to maintain sealing engagement with the drill
string yet strong enough to withstand the pressures
associated with drilling operations.
The stripper rubber 12 is mounted within the axial
passageway 14 of the drilling head 10 so as to be supported
on top of a bearing assembly 16. The stripper rubber 12
includes combination stripper body 18 and a drive bushing 20
for mounting the stripper rubber 12 within the drilling haad
10. In the prior known stripper rubbers, the stripper
rubber was separately bolted to the dri~e bushing. In a
preferred embodiment of the present invention, the drive
bushing 20 and stripper body 18 are formed in combination hy
molding the stripper 12 directly to or around the drive
bushing 20. In one form of the integral drive bushing 20,
an appendage 22 extends into the stripper body 18 to enhance
securement. In a still further embodiment, the appendage 22
may include ribs 24 (Fig. 7) which enhance the bond of the
stripper body 18 to the drive bushing 20. The drive bushing
includes a clamping flange 26 to facilitate secure
mounting within the drilling head 10.
Referring now to Figures 1 through 4, a first
embodiment of the reinforced stripper rubber 12 is there
shown. Molded at least partially within the stripper body
2 ~
18 is restraining means 30 to prevent the stripper rubber 12
from extruding, inverting or generally deforming under the
extreme borehole pressures. The restraining means 30
substantially reduces the tensile and compressive stresses
upon the stripper rubber 12 while eliminating extrusion
under pressure, particularly as the drill string is pulled
through the axial passageway 32 of the stripper rubber 12.
The restraining means 30 of the f irst embodiment
incorporates at least two pair of support members 36.
Rein~orcing cords 34 may also be incorporated into the
stripper body 18. The cords 34 are radially spaced within
the stripper body 18 in a substantially cylindrical
configuration and extend longitudinally through the stripper
body 18 to incr~a~e the longitudinal strength of the
stripper 12~ The cords 34 are preferably secured to
imbedded rings molded into the stripper body 18 coaxially
with the passageway 32. A first end of the cords 34 are
secured to a lower imbedded ring 38 by wrapping the cords 34
around the ring 38. Similarly, a second end of the cords 34
are secured to an upper imbedded ring 40 proximate the drive
bushing 20. Spacer members 42 may also be incorporated into
th~ stripper body 18 for added support. The spacer members
42 engage both the drive bushing appendage 22 and the upper
im~edd~d ring 40 to provide radial support to the upper ring
40 and therefore the reinforcing cords 34. In a preferred
embodiment, six to eiyht spacers 42 are incorporated into
the stripper body 18.
While the cords 34 and associated rings are fully
imbedded within the stripper body 18, the support members 36
of the first embodiment arP only partially imbedded therein.
The support members 36 are preferably positioned on opposite
sides of the stripper rubber 12 as shown in Fig. 3. The
supports 36 extend longitudinally to engage the drive
bushing 20 at theix upper end and the lower imbedded ring 3~
-` 2 0 ~
at their lower end to maintain the longitudinal spacing and
therefore prevent the lower e~d of the stripper rubber from
inverting or extruding upwardly. Of course, any number o~
support members 36 may be incorporated into the stripper
rubber 12 although i~ has been found that no more than two
are necessary.
In a second embodiment of the stripper rubber 12 shown
in Fig. 5, the reinforcing cords are eliminated to increase
the radial flexibility of the stripper body 18. However,
the stripper body 18 is supported lon~itudinally by the
support members 36 which extend between the drive bushing 20
and the lower imbedded ring 38. As is shown in Fig. 5, the
lower imbedded ring 38 preferably includes a shoulder 43 to
engaye the lower end of the support members 36.
A third embodiment of the reinforced stripper rubber 12
is shown in Fig. 6. The drive bushing 20 i5 formed as part
of a cylindrical can 44 within which the stripper body 18 is
mounted. The stripper body 18 has an outer cylindrical
surface which is bonded within the cylindrical can 44. The
lower end of the can 44 is provided with an annular flange
46 which is imbedded into the stripper body 18 to provide
added securement of the stripper body 18 within the can 44
particulaxly as the drill string i5 drawn through the
passageway 32 which tends to pull on the stripper body 18.
Radial deflection is accommodated by allowing the rubber to
flow vertically as a tool joint passes through the stripper
rubber 12.
Thus the present invention provides a reinforced
stripper rubber which prevents deformation and inversion
even under extreme pressures. Longitudinal support reduces
the tensile and compressive forces associated with movement
of a drill string through the stripper rubber.
Additionally, radial support can be provided by adding
radially spaced reinforcing cords.
,
~,
The foregoing detailed description has been given for
clearness of understanding only and no unnecessary
limitations should be understood therefrom as some
modifications will be o~vious to those skilled in the art
without departing from the scope and spirit of the appended
claims.
What is claimed is:
.,
:
, . , ' .
,
